Switching arrangement for a radiation guide

ABSTRACT

The radiation guide switching arrangement having at least one radiation guide switch is produced from a sandwich wafer. The sandwich wafer has a substrate, a covering layer and an electrically insulating intermediate layer. Each radiation guide switch has a moveable switching part ( 7 ) as well as at least two radiation guide ends ( 6 ), which come to rest in a plane and are arranged closely adjacent to one another such that radiation which emerges from one radiation guide end ( 6 ) can be blocked on its optical path to another guide end ( 6 ), or can be reflected into this other guide end, by means of the switching part ( 7 ). The intermediate space ( 5 ) which accommodates the switching part ( 7 ) between the guide ends ( 6 ) is filled with an index matching liquid ( 87 ) which has a predetermined refractive index, and the radiation-carrying core ( 8 ) of each radiation guide ( 49 ) is designed to taper such that radiation collimation ( 14 ) can be achieved by interaction with the refractive index of the index matching liquid ( 87 ) and the free core profile ( 13 ) in the space which is filled with liquid.  
     The switching part ( 7 ) may be mirrored on both sides, in which case one particular feature is aimed at the mirror surfaces ( 74   a   , 74   b ) which are produced in an etching process always running at right angles to a plane in which radiation guide ends ( 6 ) and their optical axes lie. This verticality is achieved by the use of sacrificial webs in the etching process.  
     A radiation guide switch produced in such a way has low radiation losses with a good switching response. In addition, a number of switches may be combined to form a matrix-like switch arrangement.  
     An attenuating unit, or a matrix-like attenuating unit, may be designed analogously to the radiation guide switches.

TECHNICAL FIELD

[0001] The invention relates to a radiation guide switch arrangement asclaimed in the precharacterizing clause of patent claim 1, and to amethod for producing it as claimed in the precharacterizing clause ofpatent claim 10.

PRIOR ART

[0002] A radiation guide arrangement is known from WO 98/12589. Theknown arrangement has four optical fiber insert channels, which runtoward one another in the form of a star, with optical fibers insertedin them. A moveable switching part was arranged at the intersectionpoint of the projection of the fiber ends. The switching part could bewithdrawn from the intersection point, as a result of which it was thenpossible for light to be transmitted between any two opposite opticalfiber ends. This light transmission was inhibited when the switchingpart was inserted. Since the switching part was mirrored, lighttransmission then occurred via the mirror surface between two adjacentfiber ends arranged at 90° to one another.

[0003] The switching part was arranged in a holder which was in the formof filigree and had two pairs of leaf springs arranged one behind theother on the left and right. The longitudinal faces of each leaf springhad a first comb structure, which engaged in a second comb structurethat was arranged in a fixed position on a base plate. The combstructures could be attracted to one another or repelled from oneanother by applying an electrical voltage, by which means the switchingpart was drawn in or drawn out at the intersection point. A mechanicalstop was provided on the leaf springs for each defined position of theswitching part.

DESCRIPTION OF THE INVENTION OBJECT OF THE INVENTION

[0004] The object of the invention is to provide a radiation guideswitching arrangement which has low radiation losses, or exactlyadjustable radiation losses, with a good switching response.

ACHIEVEMENT OF THE OBJECT

[0005] The object is achieved by producing a radiation guide arrangementhaving at least one radiation guide switch from a sandwich wafer with asubstrate, a covering layer, and an electrically insulating intermediatelayer. Each radiation guide switch has at least one moveable switchingpart as well as at least two radiation guide ends which come to rest ina plane. The radiation guide ends are arranged closely adjacent to oneanother such that radiation which emerges from one radiation guide endcan be blocked on its optical path to another guide end, or can bereflected into this other guide end, by means of the switching part. Theintermediate space which holds the switching part is, according to theinvention, filled with an index matching liquid having a predeterminedrefractive index. Furthermore, the core of each radiation guide, whichcarries the radiation, is designed to taper such that radiationcollimation can be achieved by interaction with the refractive index ofthe index matching liquid and the free core profile in the space whichis filled with liquid.

[0006] It is thus not sufficient to arrange the radiation guide ends asclose to one another as possible. The end region of each radiation guideand the refractive index of an index matching liquid between theradiation guide ends should be matched to one another so as to ensuregood radiation transmission between the radiation guide ends. In orderto achieve good radiation transmission, the guide ends are designed, andthe corresponding index matching liquid is chosen, such that theradiation which emerges from one guide end is passed to the other guideend with only low losses. Radiation guidance with losses that are as lowas possible can be achieved in the free space (which is filled withindex matching liquid) between the ends if the beam which emerges fromthe guide end can be passed to the other guide end with the same beamdiameter. This means that a collimated beam must emerge from the guideend. Radiation collimation is achieved by designing the guide core whichcarries the radiation such that it tapers in its end region, and bysearching for the index matching liquid such that its refractive indexfor the radiation which is to be transmitted in the radiation guideresults, together with the core profile, in the desired lens effect forradiation collimation.

[0007] The refractive index of the index matching liquid should at mostbe of equal magnitude to refractive index of each radiation guide core.The refractive index of the liquid is preferably chosen to be between99.90% and 98.00% with respect to the core refractive index. Very goodresults can be achieved with a refractive index between 99.4% and 98.6%.If the distance between the guide ends is short (in the region of 30μm), a good value of the refractive index is obtained in the region of99.1% (at 25° C.). This value allows stable coupling at a temperaturerange between −10° C. and 85° C. at a wavelength of between 1250 nm and1630 nm. This value should increase if the distance is greater.

[0008] The radiation guide switching arrangement according to theinvention also makes use of radiation guide switches with a mirroredswitching part. If a switching part such as this is used, then, on theone hand, it is possible to “pass on radiation” between mutuallyopposite radiation guide ends when the switching part is withdrawn fromthe intermediate space, as already indicated above. When the switchingpart is inserted into the intermediate space, the passing on ofradiation is interrupted; however, radiation which emerges from aradiation guide can now be reflected (passed on) into another radiationguide. If passed on “straight”, the collimated beam emerges from the oneguide and enters the opposite guide. If not, the collimated beam isdeflected by the mirror. In order that this switching operation canoperate with minimal radiation losses, the radiation guide ends as wellas the mirrored surface must be positioned exactly. To do this, all theradiation guide ends to be switched are located in a plane. The mirrorsurfaces of the switching part must then be positioned at right angleson this plane. It has now been shown that a mirrored switching partwhich was produced according to the method described in WO98/12589 hadmirror surfaces which are not at right angles, which then led toadditional radiation losses between two guide ends.

[0009] It has now been found that those surfaces of the switching partfrom WO98/12589 which are not at right angles were a result of theetching process described there. In contrast to WO98/12589, asacrificial web is now in each case produced at a short distance infront of the mirror surfaces which are to be produced by etching. Thisgreatly reduces any space holding etching ions in front of the mirrorsurfaces to be produced, thus making it possible to prevent, or greatlyminimize, oblique etching. Mirror surfaces produced in this way are nowat right angles.

[0010] The expression a good switching response does not just mean thatthe radiation is transmitted with losses that are as low as possiblewhen the switch is in the “switched-on position”. The switching timesmust also be reproducible, and it must be possible to carry out theswitching operations quickly. However, this also refers to switchingprocesses by means of which a predetermined attenuation can be set.However, the switching times in the case of the radiation guide switchknown from WO98/12589 differed; furthermore, high voltages had to beapplied to the comb structure of each holder having a switching part, inorder that it was possible to overcome the “tearing free effect” fromone switching position to the other.

[0011] It has been possible to eliminate this “tearing free effect” inthe embodiment described below since two identical comb structureengaging in one another have no longer been used, and, instead the tineend region of one of the two comb structures has a region with abroadened cross section. This thus results in a second fixed-positioncomb structure which matches the first comb structure. The comb tines ofthe second comb structure are arranged with a gap with respect to thefirst comb structure. A first and a second electrical voltage can beapplied to the two comb structures in order to produce an electrostaticmovement. It is now possible to configure the region with a broadenedcross section, that is to say to design it with an electrostatic voltageapplication, such that the switching part can be held in a stableposition.

[0012] At least one leaf spring element is firmly connected to theholder. The leaf spring elements are designed such that they runapproximately at right angles to the movement direction of the holder.

[0013] In addition, it has been shown that this configuration, whichwill be described in more detail in the following text, made it possiblefor the index matching liquid to be displaced out of the intermediatespaces between the tines easily. This resulted in a faster switchingresponse than the switch in WO98/12589.

[0014] The electrostatic force between adjacent tines in the first andsecond comb structures depends on the width of the gap between thesetines. With a conical, arrow-shaped tine configuration, the gap widthvaries to a greater extent with the mutual separation between the twostructures than in the case of tines of the same thickness, as inWO98/12589. For this reason, there was no need for the movement stops asin WO928/12589; surprisingly, there is now no longer any tearing freeeffect.

[0015] The switching part may also be designed without being mirrored.It can then be inserted into a radiation-carrying space in theintermediate space between two respective guide ends so as to achieve apredetermined radiation attenuation. The attenuating part of theswitching part, which can be inserted into the radiation-carrying space,is preferably provided with a metal coating. Furthermore and inparticular, the attenuating region of the switching part is no longerarranged at right angles to the aligned axis of the two guide ends, butat an angle α of less than 65°. and preferably of less than 50°. Thismakes it possible to reduce polarization-dependent attenuation resultingfrom the inserted attenuating part.

[0016] Instead of having to operate with just one switching part asstated above, a number of switching parts may be used in a singleradiation guide switch. Each switching part can then be moved in frontof in each case two radiation guide ends of two radiation guides suchthat radiation coupling and attenuation respectively is possible. Theswitching parts are preferably associated with the radiation guide endssuch that output radiation from a number of radiation guide ends can ineach case be coupled individually into a single radiation guide end,depending on the switching position of one of the switching parts.Furthermore, the arrangement may optionally be designed such that theoutput radiation from a single radiation guide end can in each case becoupled individually into one of the other radiation guide ends,depending on the switching position of one of the switching parts.

[0017] A fluid-tight housing with fluid-tight bushings for the radiationguides and the electrical cables is preferably provided. The interior ofthe housing is then filled with the index matching liquid, except for agas bubble. The volume of the gas bubble is predetermined such that anypressure in the interior of the housing resulting from thermal effectsis not greater than or less than a predetermined value.

[0018] Instead of producing a single radiation guide switchingarrangement, a number of switches can be produced which are arrangedlike a matrix in one plane, preferably on a first chip. In particular,this chip has integrated electrical guide subelements for electricalvoltages which can be applied to the switches. A second chip, which isin the form of a waveconductor chip and is preferably applied using flipchip technology, is then provided for the optical and, preferably, theelectrical connections between the switches.

[0019] The radiation guide switching arrangement having at least oneradiation guide switch, which has one switching part, is produced from asandwich wafer. The sandwich wafer has a substrate, a covering layer andan electrically insulating intermediate layer. As has already beenstated above, the switching part can be moved in front of at least tworadiation guide ends which lie in a plane. The radiation guide switchingarrangement, inter alia with the switching part and the guide channelsfor the radiation guides and their ends, is produced by means of anetching process from the sandwich wafer. The etching process is used toproduce at least one sacrificial web in the immediate vicinity of eachof the outer faces of the switching part, which run at right angles tothe plane, in order to avoid the outer faces having a profile whichdiffers from the normal to the plane.

[0020] The sandwich wafer has a covering layer which is composedessentially of silicon and whose unmasked areas are removed in an ionetching process. Each sacrificial web is at a distance of approximately10 μm, with a distance tolerance of −5 μm to +20 μm, for a coveringlayer thickness of approximately 73 μm with a thickness tolerance of ±3μm.

BRIEF DESCRIPTION OF DRAWINGS

[0021] Examples of the radiation guide switching arrangement accordingto the invention and of its production will be-explained in more detailin the following text, with reference to the figures. Further advantagesof the invention will become evident from the following descriptiontext. In the figures:

[0022]FIG. 1 shows a plan view of a radiation guide switch in theradiation guide switching arrangement according to the invention,

[0023]FIG. 2 shows a longitudinal section through mutually oppositeradiation guide ends of the arrangement illustrated in FIG. 1,illustrated in enlarged form in order to explain radiation collimationbetween the guide ends,

[0024]FIGS. 3a and 3 b show a variant of the radiation guide switch asshown in FIG. 1, which can be used in a preferred manner in amatrix-like radiation guide switching arrangement as shown in FIGS. 9 to11, with FIG. 3a showing a radiation guide switch with the switchingpart inserted, and FIG. 3b showing a radiation guide switch with theswitching part withdrawn,

[0025]FIGS. 4a to e show a schematic illustration of a number ofpossible comb structures for a radiation guide switch and the profile ofan electrostatic force F which can be produced by it, as a function ofthe comb tine end separation x in the structure, with

[0026]FIG. 4a showing a comb structure as is known from WO98/12589 withidentical thin comb tines,

[0027]FIG. 4b showing a comb structure with a row of tines whose tinesare identical to those in FIG. 4a, and the other row of tines has acuboid cross section which is arranged on a narrow tine web,

[0028]FIG. 4c showing a comb structure with a row of tines whose tinesare identical to those in FIG. 4a, and the other tine row having tineswhich are analogous to the second row of tines in FIG. 4b, but with thefree tine ends tapering (being arrow-shaped),

[0029]FIG. 4d showing a comb structure with a row of tines whose tinesare analogous to those in FIG. 4c; just with the “arrow-shaped”transition being replaced by a stepped transition, and

[0030]FIG. 4e showing a comb structure with rows of tines analogous tothose in FIG. 4b, but with the tines in one row additionally having atransverse web,

[0031]FIG. 5 shows a cross section through a masked SOI wafer forproducing the radiation guide switch according to the invention,

[0032]FIG. 6 shows a cross section analogous to FIG. 5, but aftercarrying out a deep anisotropic reactive ion etching process step,

[0033]FIG. 7 shows a cross section analogous to FIGS. 5 and 6, but aftercarrying out a further etching step in order to produce the radiationguide switch according to the invention, with the sacrificial webs alsobeing removed in this step, in order to ensure verticality of theswitching part surfaces,

[0034]FIG. 8 shows a cross section through a radiation guide switchingarrangement which is encapsulated such that it is fluid-tight,

[0035]FIG. 9 shows a plan view of a switch chip having sixteen radiationguide switches arranged like a matrix,

[0036]FIG. 10 shows a plan view of a conductor chip which can beconnected by means of flip chip bonding to the switch chip illustratedin FIG. 9,

[0037]FIG. 11 shows a cross section through the matrix-like radiationguide switching arrangement, produced using flip chip technology, alongthe lines XI-XI in FIG. 9,

[0038]FIG. 12 shows a schematic illustration of a radiation guidearrangement which can be used as an attenuating unit, in a switchingposition with basic attenuation,

[0039]FIG. 13 shows the attenuating unit, as illustrated in FIG. 12,with a predetermined attenuation produced by an attenuating part whichhas been inserted by a predetermined amount,

[0040]FIG. 14 shows an array-like arrangement of attenuating units asillustrated in FIGS. 12 and 13, and

[0041]FIG. 15 shows a variant of the radiation guide switches, as shownin FIGS. 1 and 9, having a number of switching parts.

APPROACHES TO IMPLEMENTATION OF THE INVENTION

[0042] The radiation guide switch 2, according to the invention, of aradiation guide switching arrangement 4 and as illustrated in FIG. 1 hasbeen produced as a sandwich wafer from an SOI wafer 39 (silicon oninsulator) by means of a production method as described in the followingtext. The radiation guide switch 2 has four radiation guide insertchannels 1.1 a to 1.1 d, which are arranged at right angles to oneanother and into which, once the switch has been produced, radiationguides 49 can be inserted which are provided with points and tapertoward the fiber end in accordance with the following description. Allthe radiation guide insert channels 1.1 a to 1.1 d lie in a single planeand run to a central space 5.1 in which a switching part 7.1, whose sidesurfaces are in this case mirrored, engages such that it can move. Whenthe switching part 7.1 is inserted into the space 5.1, signals can thenbe transmitted between the radiation guides which are inserted into theinsert channels 1.1 a and 11.d, as well as 1.1 b and 1.1 c. When theswitching part 7.1 is withdrawn, signals can be transmitted between theradiation guides which are inserted into the insert channels 1.1 a and1.1 c, as well as 1.1 b and 1.1 d. FIG. 1 shows the switching part 7.1in an intermediate position, with no voltage applied.

[0043] In addition to the side walls of the switching part 7.1, thereare also two sacrificial webs 3 a and 3 b in this case, which areremoved before operation of the radiation guide switching arrangement 4,as described in the following text. The radiation guides 49 are insertedinto the radiation guide insert channels 1.1 a to 1.1 d such that thecore, which carries the radiation, of each radiation guide in each casecomes to rest immediately in front of the relevant side wall of theswitching part 7.1 which in this case, by way of example, is mirrored.

[0044] The switching part 7.1 of the radiation guide switch 2 can bepushed into and out of the space 5.1 through a slot 18.1. Depressionsproduced by the etching are shown in black in FIG. 1. The switching part7.1 is arranged on a filigree holder 19.1, which can be moved in itslongitudinal axis direction in the slot 18.1. The components of theradiation guide switch 2 explained in the following text will beoutlined only briefly here, and will be described in detail later, withreference to the radiation guide switch 20 illustrated in enlarged formin FIGS. 3a and 3 b. In each case one supporting bar 21.1 a and 21.1 b,which extends on both sides and likewise has a filigree structure, isarranged on the holder end opposite the switching part 7.1, as well asapproximately in its center, at right angles to the longitudinal axis ofthe holder 19.1. A comb structure 22.1 a to 22.1 b with first comb tines23 a and 23 b, respectively, which point away from the space 5.1, isformed on each of the bar longitudinal faces. Second, fixed-positioncomb tines 24 a and 24 b, respectively, are arranged with a gap withrespect to the first comb tines 23 a and 23 b, respectively. This combtine arrangement is illustrated in enlarged form in FIG. 4c, and itselectrostatic force effect is described in the following text. Mutuallyopposite comb tines 23 a and 24 a, as well as 23 b and 24 b, of theradiation guide switch 2 have different designs. The comb tines 23 a and23 b, respectively, are in the form of straight small rods, and theopposite comb tines 24 a and 24 b are thickened in the tine end region.They taper conically toward the tine end, so as to produce an appearanceof an arrowhead, and so that the row of comb tines produces theappearance of an avenue of trees. A U-shaped leaf spring 51 a, 51 b, 52a and 52 b, which in each case has two leaf spring elements, is arrangedon each of the supporting bars 21.a and 21 b, on both sides of theholder 19.1.

[0045] The radiation guide 2 has two covering layer areas 60 and 65,which have bonding markings 61 a to 61 c and are used as an electricalconnection for an electrical voltage that acts on the comb structure22.1 a and 22.1 b. The comb tines 24 a and 24 b are connected to thecovering layer area. The comb tines 23 b in the comb structure 22.1 bare connected to the covering layer area 60 via the leaf springs 51 aand 51 b as well as the supporting bar 21.1 a. The electrical connectionfor the comb tines 23 a of the comb structure 22.1 a is provided by thesupporting bar 21.1 a, via the holder 19.1 and the supporting bar. Theswitching part 7, the holder 19, the supporting bars 21 a and 21 b, andthe comb tine arrangement 23 a and 23 b, respectively, arranged on thelatter are held in a floating manner on the covering layer 60 via ineach case two spring elements 51 a and 51 b, as well as 52 a and 52 b,which are formed in pairs to the left and right of the holder.

[0046] A monomode guide is preferably used as the radiation guide 49, asillustrated in FIG. 2. The radiation guide 49 is composed of quartzglass, whose core 8 is doped differently to the cladding 9 a and whoseouter cladding 9 b is a plastic protective sleeve. The radiation guides49 are etched using a solution in which one part of 40 percenthydrofluoric acid is buffered with ten parts of 40 percent ammoniumfluoride and 60% water. The profile obtained by the etching process isillustrated in FIG. 2. The core cladding 9 a, which has a constantdiameter of 125 μm, merges in a conical transition 11 into a corecladding end region 12, which has an approximately constant diameter ofapproximately 25 μm, is thin and tapers as a result of the etchingprocess. The approximately 8 μm thick core 8 ends in a conical tip 13.As stated in the following text, the tips 13 interact with an indexmatching liquid 87, which surrounds the tips 13, as a collimator, whichcouples the radiation that emerges from the core 8 at the tip 13 as aparallel beam 14 into the core 8 of the respective opposite radiationguide 49. The radiation which is reflected on the tapered core claddingtransition 11 is, however, reflected back at an angle which is too largefor it still to be carried in the core 8 of the guide. This radiation isthus refracted by the cladding 9 a, and is thus lost-; back reflectionsare thus suppressed to a major extent, thus resulting in an excellentreturn loss.

[0047] The contour of the core cladding 9 a shown in FIG. 2a with atwo-stage taper is chosen in particular to allow the radiation guideends 6 to be positioned as close to one another as possible in the space5.1. Core cladding 9 a with the original diameter would make thisimpossible. In order to produce the contour which is shown in FIG. 2,the plastic protective sleeve 9 b is removed over a length ofapproximately 20 mm. The glass fiber is then broken by means of a fiberbreaking tool at a distance from the end of the outer cladding that isintended to correspond to the thin diameter 12, thus producing a clean,broken surface. If etching is now carried out, then the plasticprotective sleeve 9 b which still remains forms an etching mask, and theetching liquid can reach only the projecting end of the glass fiber.However, during the etching process, the etching liquid penetrates alongthe transition between the glass fiber and the protective sleeve 9 a/9b, thus achieving the desired conical transition 11.

[0048] The refractive index of the core 8 of the radiation guide 49 is1.445. The index matching liquid should have a preferred refractiveindex of 1.43 to 1.44. Ethylcyclohexane, cyclododecane, butyrolacetone,cyclohexane, cyclohexyl acetate, tert-butylcyclohexane and decanonitrilemay be used, by way of example, as liquids with a refractive index suchas this. If the index matching liquid is heated, it is also possible touse, by way of example, limonene, myrcene and decalin with a refractiveindex of more than 1.45; heating reduces the refractive index. Octane,octene, silicone oils, decane and dodecane, which have a refractiveindex of less than 1.42, are less suitable but may still be used, by wayof example.

[0049] A number of (in this case three) sprung lugs 16 are formed oneach side wall 15 a to 15 b of the radiation guide insert channels 1.1 ato 1.1 d in FIG. 1. These lugs 16 now press the inserted radiationguides 49 against the other opposite channel wall 17.1 a, 17.1 b, 17.1 cand 17.1 d, respectively. The corresponding radiation guide 49 is inthis way clamped firmly in the channel 1.1 a to 1.1 d. The insertionresistance, caused by these lugs 16, is low.

[0050] Between the [lacuna] on the two arrangements—spring elements,supporting bars, comb structure 51 a, 51 b, 21 a, 22 a and 52 a, 52 b,21 b, 22 b—the slot 18 which accommodates the holder 19.1 has recesses63 and, offset with respect to them, the holder 19 has studs 64. Therecesses 63 and the studs 64 are arranged symmetrically with respect tothe holder axis and with respect to the center line of the slot 18.1.The overall width, measured over two studs 64 which are arranged to theleft and right of the holder shaft, is less than the width of the slot18.1 only by a tolerance. The studs 64 and the recesses 63 are arrangedwith respect to one another, when the switching part 7.1 is in the restposition, such that the larger portion of the length of the studs 64 islocated in the part of the gap 18.1 where there is no recess, and only asubregion of the studs, which corresponds to the longitudinal directionof the holder movement in the switching process, is located above therespective recess 63. If an electrical voltage is now applied betweenthe covering layer area 60 and the covering layer area 65, then anelectrostatic attraction force is produced, as described above, via thecam structure 22.1 a and 22.1 b as well as via the studs 64 and the“recess structure” on the holder 19.1.

[0051] Details of the radiation guide switch 2 are described in FIGS. 3aand 3 b with reference to a radiation guide switch 20. The radiationguide switch 20 is designed analogously to the radiation guide 2.However, it is designed such that it remains electrically on the onehand in an inserted “active” equilibrium position (in which signals aretransmitted between radiation guides in the channels 1.2 b/1.2 c and 1.2a/1.2 d which are analogous to the channels 1.1 a to 1.1 d) when adifferent voltage is applied and, in a further position, in a pushed-out“active” equilibrium position (in which signals are transmitted betweenradiation guides in the channels 1.2 a/1.2 c and 1.2 b/1.2 d). Theradiation guide switch 20 is shown in a position with respect to theposition of the radiation guide 2 and is used together with a furtherfifteen radiation guide switches in the switch chip 127 described in thefollowing text. Analogous elements of the radiation guide switch 2 and20 are annotated by the same reference symbols, but distinguished by“0.1” for the radiation guide 2 and with “0.2” for the radiation guide20.

[0052] The switching part 7.2 of the radiation guide switch 20 can bepushed into and out of the space 5.2 through a slot 18.2. It is arrangedon a filigree holder 19.2, which runs in the slot 18.2. One supportingbar 21.2 a and 21.2 b, which extends on both sides and likewise has afiligree structure, is arranged on each holder end, at the opposite endof the switch part 7.2, as well as approximately in its center, at rightangles to the longitudinal axis of the holder 19.2. A comb structure22.2 a to 22.2 b with first comb tines 23.2 a pointing away from thespace 5.2 and with a row of comb tines 24.2 b pointing toward the space5.2 is formed on each of the bar longitudinal faces. Second,fixed-position comb tines 24.2 a and 23.2 b, respectively, are arrangedwith a gap with respect to the first comb tines 23.2 a and 24.2 b,respectively. The comb tines 23.2 a, 23.2 b, 24.2 a and 24.2 b areidentical, but mutually associated pairs are in mirror-image form withrespect to one another, as is illustrated in FIG. 4d.

[0053] The electrostatic forces which act on the rows of comb tines whenan electrical voltage is applied are described in the following text andin FIGS. 4a to 4 e.

[0054] The spring element pairs 107 and 109 hold the holder 19.2 andthus the switching part 7.2. FIG. 3a shows the switching part 7.2 in aposition in which it is pushed out into the space 5.2, and FIG. 3b showsit in a drawn back position. As already described above, when in thepushed-out position, radiation reflection occurs on the mirrored sidesurfaces 74 a and 74 b of the switching part 7.2.

[0055] Furthermore, the radiation guide switch 20 has four electricalcontact surfaces 111 to 114. The contact surface 111 is electricallyconnected to the holder 19.2 in the area 50 a via the one spring elementof the spring element pair 107, and is thus connected to the tines 24.2b and 23.2 a, respectively, which are arranged on the supporting bars21.2 a and 21.2 b. It should be mentioned here that the tines 23 a and23 b of the radiation guide switch 2 which are arranged on thesupporting bars 21.1 a and 21.1 b point away from the space 5.1, whilethe tines 24.2 b which are arranged on the supporting bar 21.2 a of theradiation guide switch 20 point toward the space 5.2, and the tines 23.2a which are arranged on the supporting bar 21.2 b point away from it.

[0056] The contact surface 113 is connected to the holder 19.2, and thusto the tines 23.2 a and 24.2 b, in the area 50 b via the other springelement of the spring element pair 109. The two contact surface 111 and113 are connected to one another via the holder 19.2.

[0057] The contact surface 112 is electrically connected to thefixed-position tines 23.2 b. The free ends of these tines 23.2 b pointaway from the space 5.2. The contact surface 114 is electricallyconnected to the fixed-position tines 24.2 a. The free ends of this rowof tines 24.2 a point toward the switching part 5.2.

[0058] When no voltage is applied, adjacent tines 23.2 b/24.2 b as wellas 21.2 b/24.2 a each half overlap a respective comb structure 22.2 aand 22.2 b. The switching part 7.2 is located in a switchingintermediate position. When appropriate voltages are applied, theradiation guide switch 20 can be moved on the one hand to the positionshown in FIG. 3a, and on the other hand to the position shown in FIG.3b. If the voltage +V₀ is applied to the contact surface 114, −V₀ isapplied to the contact surface 112, and a ground voltage (0V) is appliedto the contact surfaces 111 and 113, then the switching part 7.2 has astable position not only in the position shown in FIG. 3a but also inthe position shown in FIG. 3b.

[0059] In order to switch from the position of the switching part 7.2illustrated in FIG. 3a to that illustrated in FIG. 3b, the electricalvoltage on the contact surface 114 is increased by ΔV to +V₀+ΔV. At thesame time, the electrical voltage on the contact surface 112 isincreased by ΔV to −V₀+ΔV and, in addition, the voltage −ΔV is appliedto the contact surfaces 111 and 113, resulting in switching to theposition shown in FIG. 3b. Switching in the opposite direction takesplace when the voltage states mentioned initially are assumed onceagain.

[0060] In order to ensure that signals are transmitted with losses thatare as low as possible between the radiation guide ends, the core endsof the radiation guides 49 are designed appropriately in accordance withthe above embodiment, and the space 5.1 (and 5.2) is filled with anindex matching liquid. However, this liquid also propagates, coming fromthe central space 5.1, to the comb structures 22.1 a and 22.1 b. Inorder to achieve short switching times despite the presence of theliquid in the comb structures 22.1 a and 22.1 b, their comb tines aredesigned as illustrated in enlarged form in FIG. 4c. The comb tines 24.1a and 24.1 b, respectively, have a conically thickening part 25, whichis arranged on a thin web 26 as a tine foot. This refinement allows theindex matching liquid to be forced easily out of the narrow gap when thetwo comb tine arrangements with the tines 23.1 a and 24.1 a as well as23.1 b and 24.1 b, respectively, are moved with respect to one another.The friction resistance in the index matching liquid is reduced, whichleads to a shorter switching time.

[0061] The comb tine shape chosen here also has another advantage,however. The movement distance of the two comb tine arrangements isself-limiting; there is therefore no need for a stop, as is absolutelyessential in WO98/12589 (indicated there by the reference symbols 36 and38). This also eliminates a source of faults, such as that which occursin particular as a consequence of adhesion on the stops in the switch inWO98/12589.

[0062] This is because the electrostatic force that is produced isinversely proportional to the gap between the comb tines of the two combtine arrangements. Specifically, the gap becomes larger here after themaximum movement of the comb tine arrangement, so that the forceincrease is sharply reduced. Minor fluctuations in the switching voltagethus now have scarcely any influence on the movement distance.

[0063] In order to illustrate this statement, FIGS. 4a, 4 b, 4 c, 4 dand 4 e show the electrostatic forces between difference comb tinearrangements. Each figure shows the comb tine arrangement on theright-hand side and the force F between the two tine arrangements on theleft-hand side, with a constant DC voltage and with the separationbetween the tine ends being x. If the distance is x=0, the free tineends of the one comb tine arrangement are in a line with those of theother comb tine arrangement. The further the tines engage in oneanother, the greater x becomes. x is a measure of the distance by whichthe tines engage in one another.

[0064]FIG. 4a shows a normal comb tine arrangement, with thefixed-position tines (webs 27 a) being identical to the moving tines(bars 27 b), that are used, by way of example, in WO98/12589. The forceF₁ acting on the tine arrangement 27 a/b is shown in the force/movementdiagram 30.1 on the left. The force F₁ which acts on the arrangement isinitially zero, when the tine ends are at a certain distance a₁ from oneanother. Starting with the tine ends being aligned with one another butwith a gap [x₁=0], the force F₁ which acts on the comb structure withthe tines 27 a and 27 b is constant over a wide range A₁ of theinsertion of the tines 27 a and 27 b into one another. However, it risessharply [region D₁] when the free tine ends approach the respectiveopposite connecting bars 29 a and 29 b, respectively, for the tine feet.An arrangement such as this should be operated with a mechanical stop,as is actually also the case in WO98/12589.

[0065]FIG. 4b show a tine arrangement in which the moving tines 31 b aredesigned analogously to those shown in FIG. 4a. The fixed-position tines31 a have a broadened web region 32 with a cuboid cross section in theirfree tine end region, however. The force F₂ which acts on the tinearrange 31 a/b is illustrated in the force/movement diagram 30.2 on theleft. The force F₂ which acts on the arrangement is likewise zero whenthe tine ends are at a certain distance a₂ from one another. Until thebroadened web regions 32 are located completely between the tines 31 b,the force F₂ is constant [region A₂]. If the tines 31 a/b are then movedfurther into one another, the narrow web part 33 which now comes intoplay results in the reduction in the force F₂ [region B₂]. Thisdecreasing region B2 is then followed by a constant force region C₂,which merges into a rapid force increase (region D₂) when, in this caseas well, the tine ends approach the opposite tine foot connecting web29.1 a or 29.2 b, respectively. This tine arrangement does not require amechanical stop; however, the displacement of the index matching liquidout of the tine intermediate spaces, as in the preferred embodimentwhich will be described in more detail in the following text, is notoptimal.

[0066]FIG. 4c shows a tine arrangement according to that which hasalready been indicated in FIG. 1. The tines 23 a and 23 b, respectively,of the moving tine arrangement are in this case identical to those inFIGS. 4a and 4 b. The fixed-position tines 24 a and 24 b, respectively,are designed analogously to the tines 31 a; in the free tine end region,the part 32 is designed such that it tapers to a tip 25. The remainingregion 37 still has a cuboid cross section. Since the gap between thebars 23 a and 23 b, respectively, which have equal widths, and the webpart 25 decreases as they move toward one another, the electrostaticattraction force F₃ rises, as shown by the curve region 40. When thetapering regions 25 are pushed in between the tines 23 a and 23 b,respectively, the force F₃ is constant (curve region 41), since there isnow no change in the gap width. The force decreases (curve region 42)only when the thin “web spike” 26 enters the region in which the freetine ends of the tines 23 a and 23 b are scattered. If the thin webspike 26 has no “edge disturbance” in the intermediate region of thetines 23 a and 23 b, respectively, the electrostatic force F₃ isconstant once again (curve region 43). This tine arrangement does notrequire any mechanical stop either, but has the advantage of shorterswitching tines than the tine arrangement shown in FIG. 4b.

[0067] Further refinement options for a tine arrangement are illustratedin the form of an associated electrostatic force/movement diagram inFIG. 4d. This tine arrangement has the same radiation guide switch 20 asthat shown in FIGS. 3a and 3 b. In contrast to the tine arrangements inFIGS. 4b and 4 c, the mutually opposite tine arrangements in this caseare identical, with in each case one tine part 34 a and 34 b, which hasa cuboid cross section on a thin tine foot 36. The force/movementdiagram associated with this tine arrangement has an analogous profile,with a few exceptions, to the force/movement diagram in FIG. 4c.However, a difference results that a constant force region A4, as shownin FIGS. 4a and 4 b, starts once again when the tine ends, which arelocated opposite one another in the gap of the other ones, are at thesame level. However, in comparison to the force/movement diagrams shownin FIGS. 4b and 4 c, there is a deeper notch in a second constant forceregion C₄ once the tine parts 34 a and 34 b have moved passed oneanother, virtually to a force F₄→0.

[0068]FIG. 4f shows a further variant of a tine arrangement. This tinearrangement is designed analogously to the tines illustrated in FIG. 4b,with the difference that there is a transverse web 44.1 in the tines44.2 which have a cuboid cross section. This transverse web 44.1 resultsin a high pull-in force in comparison to the other tine arrangements inFIGS. 4a to 4 d, and this is extremely useful for the acceleration ofthe holder which is shown in FIGS. 1, 3a, 3 b and 9.

[0069] The production of the radiation guide switch 2 or 20,respectively, as described above is based on an SOI wafer 39 asillustrated in FIG. 5. The SOI wafer 39 comprises a monocrystallinesilicon substrate 70 on which an amorphous silicon dioxide intermediatelayer SiO₂ 71 is applied. A silicon covering layer 73 is arranged on topof the silicon dioxide layer 71. This silicon covering layer 73 ismasked by means of a mask 72 corresponding to the structure shown in theform of a plan view in FIGS. 1 and 3a/b, but additionally with anexception as described in the following text. The thickness of thecovering layer 73 is chosen appropriately for the radiation guide 49which is to be inserted into the radiation guide insert channels 1.1 ato 1.1 d and 1.2 a to 1.2 b. By way of example, it is 75 μm when usingmonomode radiation guides. The substrate 70 and the covering layer 73are electrically conductive, while the intermediate layer 71 iselectrically insulating.

[0070] The exception mentioned above in masking relates to the processof etching out the switching part 7.1 or 7.2, if this is intended to beused as a mirror for the radiation of adjacent radiation guides. Theswitching states of the radiation guide switch 2 or 20 compriseradiation being passed through between mutually opposite radiation guideends in a first switching state, and radiation being passed byreflection via in each case one mirrored wall of the switching part 7.1or 7.2 in the second switching state. In order to allow these twoswitching states to be produced,

[0071] the radiation guide ends must lie in a plane,

[0072] the mutually opposite radiation guide end regions must be alignedwith one another, and

[0073] the axes of the radiation guide ends, which are connected to oneanother for signal purposes in the second switching state, must meet themirrored surface of the switching part at a single point and must havethe conjugate angle to the normal at this point.

[0074] These conditions must be satisfied with a tolerance that is assmall as possible in order to achieve a circuit with minimum radiationlosses. The above conditions furthermore mean that the optical axes ofthe end regions of the radiation guide must intersect at that point, andeach mirrored surface must be arranged on one of the angle bisectors ofthe optical axis. Furthermore, each mirrored surface must be at rightangles to the plane in which the radiation guide ends are arranged. Ithas now been shown that, if the etching process as described inWO98/12589 were used, the mirrored surfaces of the switching part wouldnot be at right angles, and that mutual separation would decrease in thedownward direction. The reduction was a result of there being arelatively large space that was filled with etching ions during theetching process in the side wall region of the switching part.

[0075] In order to produce the radiation guide switch 2 or 20, theunmasked parts of the covering layer 73 are now removed in a vacuumchamber using a deep anisotropic reactive ion etching process. Thisprocess is carried out at a pressure of 2.6 Pa, at a temperature of −95°C. and with a voltage of −70 V (DC bias) between the electrode and theSIO wafer. In addition, a radio frequency of 13.5 MHz, a gas flow ofsulfahexafluoride at 200 cm³/min, of oxygen at 16 cm³/min and of CHF at10 cm³/min are used. An inductively coupled plasma is used as the ionsource.

[0076] This material removal process is continued until the unmaskedcovering layer material has been removed as far as but not including theintermediate layer 71, as is illustrated in the form of a cross sectionin FIG. 6.

[0077] In order to produce side walls 74 a and 74 b which are not atright angles, a sacrificial web 75 a and 75 b is now arranged a shortdistance in front of each switching part side wall 74 a and 74 b. Thesacrificial webs 75 a and 75 b can be seen in FIGS. 1, 5 and 6. Once theswitching part 7.1 has been produced, with side walls 74 a and 74 bwhich are now exactly vertical, the sacrificial webs 75 a and 75 b areremoved. These can be removed, using the method described in thefollowing text, by using hydrofluoric acid to etch underneath theintermediate layer 71, as a result of which they are no longer held andfall out, and by etching directly underneath in the plasma etchingsystem which is mentioned in the following text, by varying the etchingparameters so as to achieve etching along the intermediate layer 71. Athird possible way to remove the sacrificial webs 75 a and 75 b is todesign them to be so thin that they can be converted to silicon oxideduring the subsequent oxidation step (in order to reduce the roughness),and can then also be dissolved in the hydrofluoric acid while partiallyetching underneath the intermediate layer 71.

[0078] In a next method step, the intermediate layer areas 71 are nowetched underneath the thin webs 77 shown in FIG. 6, until the latter arefloating freely, using 48 percent hydrofluoric acid at room temperature.The intermediate layer areas 71 underneath the broad webs 79 are onlyetched in the form of grooves. However, the broad webs 79 remain, as isshown in FIG. 7.

[0079] The thin webs 77 then become the filigree parts as illustrated inFIGS. 1 and 3a/b. Since the switching part (mirror) 7.1 or 7.2,respectively, the holder 19.1 or 19.2, respectively, the supporting bars21.1 a and 21.1 b as well as 21.2 a and 21.2 b, respectively, the sprunglugs 16 and the spring elements 51 a/b and 52 a/b as well as 107 and109, respectively, together with their webs 57 are merely formed as afiligree structure from elements with thin widths, while these arenecessary in accordance with mechanical requirements, they are “etchedfree”. An analogous situation applies to the comb structures.

[0080] Once the entire structure has been produced, the side walls 74 aand 74 b of the respective switching part 7.1 or 7.2 may have an opticalreflection coating vapor-deposited on them.

[0081] The four radiation guides 49 are then pushed into thecorresponding radiation guide insert channels 1.1 a to 1.1 d and 1.2 ato 1.2 d. The insertion process is carried out under a microscope.

[0082] Once the radiation guides have been pushed into the appropriateradiation guide insert channels, the latter are adhesively bonded to acovering panel in the edge region of the switch arrangement. In order toensure that the adhesive can never penetrate as far as the filigreeparts, even in the event of careless handling, the radiation guideinsert channels 1 a to 1 d are connected to adhesive holding channels90, which can hold excess adhesive.

[0083] Instead of having to design the switching parts 7, 7.1, 7.2 and101 such that radiation is completely blocked or is completelytransmitted between two respective guide ends, only partial blocking canalso be provided. An element such as this is then used for definedattenuation of signal radiation. In order to achieve this aim, it wouldnow be possible to think of inserting a mirror only partially into aspace 150 carrying radiation between two respective guide ends 151 a and151 b. However, it has been found that, although this would allowattenuation, such attenuation would, however, be highly dependent on thepolarization. This means that the attenuation of the TE(transelectrical) and TM (transmagnetic) waves would differ. In order toreduce the polarization dependency, the switching part 152 is in thiscase (FIGS. 12 and 13) provided with an attenuating metallic coating.The reflection and attenuation characteristics of such a coating can becalculated, by way of example, in accordance with Born and Wolf,“Principles of Optics”, “An absorbing film on a transparent substrate”,page 628 et seqq, Pergamon Press, 1975.

[0084] The polarization dependency between the two wave types —TE and TMwaves—is due to the fact that, in the case of a diffraction arrangement,the boundary conditions on the metallized free edge of the switchingpart 152 may be different. The polarization dependency can now bereduced if the switching part 152 is no longer arranged only slightlyaway from the vertical with respect to the aligned axis 153 of the twoguide ends 151 a and 151 b, but an angle of less than 65°. Very goodresults have been achieved with an inclination of less than 50°, andpreferably at 45°.

[0085] An angle which deviates only slightly from the vertical waspreviously chosen in order that no radiation could be reflected backinto one of the guide ends 151 a or 151 b. Otherwise, it would bedesirable to achieve an arrangement that was as vertical as possible.The severe inclination (small angle) proposed here was contrary to theprior art.

[0086] The gap 154 between the guide ends 151 a and 151 b must beenlarged as a result of the angle, which has been reduced in comparisonto the prior art, between the surface of the switching part 152 and theaxis 153, which could lead to increased radiation losses between the twoends 151 a and 151 b. These losses are illustrated in FIGS. 12 and 13 byan opening beam profile 150, which is no longer received entirely by theguide core 155. However, this distance increase can be kept withinlimits by bending the attenuating part 157 at a bend point 156 in theswitching part 152.

[0087] Depending on the predetermined basic attenuation, the gap 154 mayin this case be filled with an index matching liquid, or else thisliquid may be dispensed with. A predetermined attenuation between a highvalue and a low value can now be set by means of two fixed end positionsof the attenuating part 157 within or outside the space 150 whichcarries the radiation. However, intermediate positions may also beassumed.

[0088]FIG. 8 shows, in simplified form, a radiation guide switchingarrangement 4 having only a single radiation guide switch 80, which maybe designed analogously to the radiation guide switch 2 or 20.Furthermore, only two radiation guides 81 a and 81 b are shown, for thesake of simplicity. The arrangement 4 is arranged on a base 82 and iscovered by a cover 83, which is connected to the base 82 in afluid-tight manner. The cover 83 has fluid-tight bushings 85 for theradiation guides 81 a and 81 b. The interior 86 of the radiation guidearrangement 4 is filled with an index matching liquid 87 in accordancewith what has been stated above, in order to achieve a collimated beam.Furthermore, there is a gas bubble 88 in the interior 86, whose volumeis predetermined such that any pressure in the housing interior 86resulting from thermal expansion of the index matching liquid 87 and ofthe housing walls 82 and 83 is not greater than or less than apredetermined value.

[0089] Instead of only a single radiation guide switch 2 or 100, anumber of radiation guide switches may also be used in one radiationguide switching arrangement. Once such matrix-like arrangement 120 for m“incoming” and n “outgoing” radiation guides 121 a to 121 d and 122 a to122 d has m n, in this case sixteen, radiation guide switches 100 aa to100 dd. The sixteen radiation guide switches 100 aa to 100 dd make itpossible to switch the signal flow between the radiation guides 121 a to121 d and 122 a to 122 d. An arrangement 120 such as this is illustratedin FIGS. 9 and 10, with the switching parts 101 aa−101 dd likewise beingmirrored in this case. 2 m+n or m+2 n, in this case twelve, electricaldrive connections 123 a to 123 d, 124 a to 124 d and 125 a to 125 d areprovided for driving the radiation guide switches 100 aa to 100 dd,which are arranged like a matrix.

[0090] In the radiation guide circuit arrangement 120, the radiationguide switches 100 aa to 100 dd, which are arranged like a matrix, areconnected to one another in order to drive them electrically, and theoptical connections are connected to one another in a switch chip 127(see FIG. 9), by means of a conductor chip 129 (see FIG. 10) which isapplied using flip chip technology.

[0091] Sixteen radiation guide switches 100 are applied to the switchchip 127, in an analogous manner to those illustrated in FIGS. 3a and 3b. In order to avoid overloading in FIG. 9, only the contact surfaces111 to 114 of the individual radiation guide switches 100 aa to 100 dd,as well as the holder 103 with the mirrored switching part 101, areillustrated. Furthermore, the switch chip 127 has in each case fouraligning channels 131 for introduction of the “incoming” and “outgoing”radiation guides 121 a to 121 d and 122 a to 122 d. In order to providethe electrical drive for the radiation guide switches 100 aa to 100 dd,the switch chip 127 has, on a face which is free of aligning channels,four bonding pad pairs 123 a/124 a to 123 d/124 d and, on the side whichis free of other aligning channels, four bonding pads 125 a to 125 d.Wires are bonded to these pads, and lead to the houding.

[0092] The conductor chip 129 illustrated in 10 has a number ofintegrated waveguide subelements 133 aa to 133 dd and 134 aa to 134 dd,which are aligned with one another, are arranged in a plane and are eachinterrupted by free space sections 135 aa to 135 dd. Four waveguidesubelements 133 aa−133 dd are in each case aligned with the aligningchannels 131 for the radiation guides 121 a to 121 d. The respectivefour waveguide subelements 134 aa to 134 dd are aligned with thealigning channels of the radiation guides 122 a to 122 d. The free spacesections 135 aa to 135 dd are each provided in the region of theswitching parts 101 aa to 101 dd of the radiation guide switches 100 aato 100 dd. Contact areas 143 aa to 143 dd with the contact surfaces 139to 142 are provided on the conductor chip 129 matching the respectivecontact surfaces 111 to 114. These contact surfaces are in the form ofcontacts (solder bumps) which can be soldered, and can be soldered tothe switch chip using flip chip technology. All the contact surfaces 140and 142 of the contact areas 143(a-d)a, 143(a-d)b, 143(a-d)c and143(a-d)d (vertical direction in FIG. 10) are connected to one anotherand to in each case one connection 124 a-d or 123 a-d. One contactsurface 141 is in each case connected to one contact surface 139 of anadjacent contact area in a row. The contact surface 139 which is in eachcase adjacent to the right-hand side of the conductor chip in FIG. 10 isconnected to a connection which is associated with the electricalconnection 125 a to 125 d. The contact surfaces 139 and 142 in arespective contact area 139 aa to 139 dd are electrically connected toone another, via the respective spring element 109 by means of thecontact surfaces 111 and 113, which are located on them, of theradiation guide switches 100 aa to 100 dd. FIG. 11 shows schematicallyand in the form of a cross section how, by way of example, the radiationguide 121 a, the switch chip 127 and the conductor chip 129 are joinedtogether. An electrical connection between the respective contact areas111 and 113 of the switching parts 101 aa to 101 dd is made via therespective spring element pair 107 and the holder 19.2.

[0093] In order, by way of example, to introduce the second mirroredswitching part 101 ab in the first row in FIG. 10 into the central space5 in the free space section 135 ab between the waveguide subelements 133ab and 134 ab, the voltage +V₀ is applied to the connection 124 b, andthe voltage −V₀ is applied to the connection 125 a. There is now avoltage of 2V₀ only on the radiation guide switch 100 ab, and this isable to switch the bistable suspension. Only the voltage V₀ itself ispresent on the other radiation guide switches 100 aa, 100 ac and 100 adin the first row and those switches 100 bb, 100 cb and 100 db in thesecond column, and this is not sufficient for them to switch. There isthus a “through connection” between the two radiation guides 121 a and122 b. Furthermore, FIG. 9 also shows through connections for the guides121 b and 122 c, for the guides 121 c and 122 a, as well as for theguides 121 d and 122 d.

[0094] Analogously to the matrix-like arrangement of a number ofradiation guide switches as described above, a number of attenuatingunits 160 a to 160 d may also be arranged together. The attenuatingunits 160 a to 160 d can now also be combined linearly to form aso-called array. Attenuating units 160 a to 160 d may also be arrangedtogether with radiation guide switches on a chip. The production processcan likewise be carried out by means of photolithography and an etchingtechnique. The distance between the individual attenuating units should,however, correspond to the standard distance between the radiation guideswitches described above.

[0095] In the case of fiber ribbons, a number of radiation guides arejoined together and are adhesively bonded with a separation of 250 μm.There is thus likewise a distance of 125 μm between the individualfibers, which have a standard separation of 125 μm. This distance issufficient for an “electrostatic motor” for movement of the switchingpart 152. This “electrostatic motor” is designed analogously to that ofthe radiation guide switches, as is illustrated in FIGS. 1, 3a and 3 b.In order to connect this “electrostatic motor” electrically, appropriatewire bonding must be implemented. To do this, a second printed circuitboard is arranged underneath the silicon substrate (for exampleunderneath the silicon substrate 70), with this silicon substrate havingbonding surfaces. The arrangement is now chosen such that the bondingwires in this case run in the space between the radiation guides.

[0096]FIG. 14 illustrates an array-like arrangement of in this case, byway of example, four attenuating units 160 a to 160 d. One spring part161 a to 161 d is in each case arranged separately from in each case oneelectrostatic drive 162 a to 162 d. This makes it possible to producevery narrow attenuating units, which are located between the channels163 a to 163 e for the individual radiation guides.

[0097] Instead of only a single switching part 7, 7.1, 7.2, 101 aa to101 dd and 152, it is also possible, as shown in FIG. 15, to arrange anumber of switching parts 165 a to 165 d in a single radiation guideswitch 166. In this case as well, the ends 170 a to 170 f of radiationguides 169 a to 169 f lie in a plane, in the form of beams. For the sakeof simplicity, the switching parts 165 a to 165 d are in this case shownonly with one small holder piece 166 a to 166 d; the entireelectrostatic movement device, which has already been described above,is not shown. The switching parts 165 a to 165 d are mirrored on theirunshaded face, for the radiation which is to be coupled into theradiation guides 169 a to 169 f. The radiation guide switch 166 is nowdesigned such that the radiation from the radiation guides 169 a to 169c and 169 e as well as 169 f can now be introduced by means of in eachcase one of the switching parts 165 a to 165 d into the radiation guide169 d, provided that an appropriate switching part of the switchingparts 165 a to 165 d, in this case by way of example the switching part165 a, has been pushed into the central space 171.

[0098] If, by way of example as illustrated in FIG. 15, the switchingpart 165 a has been pushed in, then radiation which emerges from theradiation guide 169 c is reflected on the mirrored surface of thisswitching part 169 a, and is coupled into the core of the radiationguide 169 d. Radiation emerging from the remaining radiation guides 169a, 169 b, 169 e and 169 f cannot be coupled into the radiation guide 169d. In order to achieve sufficient decoupling of the output radiationfrom the other radiation guides, their radiation (if it can fall ontothe reflective surface of one of the switching parts which have beenpushed in) should fall at an angle of more than 12° to the core axis. Inthe example shown here, radiation from the radiation guide 169 b alsofalls onto the mirrored surface of the switching part 165 a. Afterreflection, the radiation from the guide 169 b should then be incidentat an angle of more than 12° to the core axis of the radiation guide 169e (and, of course, also to the core axis of the radiation guide 169 d)and will then no longer be coupled into it.

[0099] In order to determine an optimum angle, reference is made to thepublication by C. M. Miller, C. Mettler, A. White in Optical FiberSplices and Connectors, Theory and Methods, New York; Marcel DekkerInc., 1986, Chapter 4. This describes a method for calculating couplinglosses between two mutually tilted and offset fibers. This theory isapplied, in a modified form, to the fiber end arrangement shown in FIG.15.

[0100] The position of the relevant switching part 165 a to 165 d is nowchosen such that optimum coupling is achieved for the two “switched”radiation guide ends in the switched state, and a coupling loss of atleast 50 dB is achieved for the other radiation guide ends.

[0101] An estimate of the coupling loss ┌ in dB can be made using theformula quoted below, the explanation of which can be found in FIG. 16.FIG. 16 shows two cores 173 and 174, which carry radiation, are tiltedthrough an angle θ with respect to one another and are offset by a valuer with respect to one another, of guide ends separated by a distance z.The coupling losses ┌ are in this case given by:$\Gamma = {{- 10}\quad {\log \lbrack {{\frac{16\quad {n_{co}^{2} \cdot n_{0}^{2}}}{( {n_{co} + n_{0}} )^{4}} \cdot \frac{1}{q}}\exp \{ \frac{p \cdot u}{q} \}} \rbrack}}$

[0102] In the above formula, n_(co) and n₀ mean the refractive index ofeach radiation guiding core and, respectively, of the material in thespace between the guide ends, that is to say generally our indexmatching liquid.

q=G ²+1, where G=z/k·w ²

[0103] According to FIG. 16, z is the distance between the relevantguide ends. w is the radius of the free beam between the guide ends, inwhich the radiation power is dropped to 1/e part of the maximum.

[0104] k=2πn₀/λ, where λ is the wavelength of the radiation in thevacuum.

p=k·w ²/2

[0105] u=F²+2F·G(sinθ)+(G²+½)sin²θ where θ is the tilt angle between thetwo guide ends. Since, however, mirrors 165 a and 165 d are interposedin the arrangement shown in FIG. 15, θ is an angle value without areflection value (correction by double addition of the reflection angleof the relevant mirror).

F=r/k·w ²

[0106] If typical values are inserted in this formula, then this resultsin a coupling loss ┌ of more than 55 dB in a wavelength band from 1250nm to 1630 nm, and with a tilt angle of 12°. This means that the coreaxis of the radiation guide ends into which radiation is no longerintended to be coupled should preferably be at a tilt angle θ of atleast 12°.

[0107] If the switching part 165 a is drawn out and the switching part165 b is pushed in, then radiation is coupled from the radiation guide169 b to the radiation guide 169 d. The switching part 165 d providescoupling from the radiation guide 169 e to the radiation guide 169 d,and the switching part 165 c provides coupling from the radiation guide169 f to the radiation guide 169 d. If all the switching parts 165 a to165 d are drawn out, radiation can be coupled from the radiation guide169 a to the radiation guide 169 d.

[0108] Instead of the radiation being coupled from the radiation guides169 a, 169 b, 169 c, 169 e and 169 f into only one radiation guide 169 dby means of the appropriate switching parts 165 a to 165 d, radiationfrom the radiation guide 169 d can also be coupled, using precisely thisarrangement, individually into the radiation guides 169 a, 169 b, 169 c,169 e and 169 f.

[0109] Two switching parts 165 a and 165 b as well as 165 c and 165 dare in each case arranged on both sides of the radiation guide 169 a,aligned with the radiation guide 169 d. The radiation guides 169 b to169 f are arranged such that they are closely adjacent. The switchingparts 165 a to 165 d could also be arranged individually between tworespectively adjacent radiation guides, although the radiation would notnecessarily be switched from and through these radiation guides.However, in comparison to the illustration that has just been sketched,the illustration shown in FIG. 15 occupies less space, so that moreradiation guides can be switched per space unit. Other configurationsare also possible in addition to the arrangement shown here and thenumber of radiation guides.

[0110] In the case of the arrangements just sketched, the central space171 is also preferably filled with an index matching liquid, but neednot be (poorer embodiment).

[0111] As stated above, the reflective surface of the switching part cannow be arranged with respect to in each case two radiation guide endssuch that the radiation can be coupled between these two radiationguides. However, further radiation guide ends may also be arranged suchthat, by way of example, two further radiation guide ends can still becoupled to one another by means of one and the same switching part.

1. A radiation guide switching arrangement (4, 120) having at least oneradiation guide switch (2, 100, 100 aa-100 dd, 166), produced from asandwich wafer (39) with a substrate (70), a covering layer (73), and anelectrically insulating intermediate layer (71), with each radiationguide switch (2, 100, 100 aa-100 dd, 166) having at least one moveableswitching part (7, 101, 101 aa-101 dd; 152; 165 a-d) and at least tworadiation guide ends (6, 133 aa-133 dd, 134 aa-134 dd; 170 a-f) whichcome to rest in a plane and are arranged closely adjacent to one anothersuch that radiation which emerges from one radiation guide end (6, 133aa-133 dd, 134 aa-134 dd; 151 a, 151 b; 170 a-f) can be blocked on itsoptical path to another guide end (6, 133 aa-133 dd, 134 aa-134 dd; 151a, 151 b; 170 a-f), or can be reflected into this other guide end, bymeans of the switching part (7.1, 7.2, 101, 101 aa-101 dd; 165 a-d),characterized in that the intermediate space (5, 135 aa-135 dd; 154;171) which holds the switching part (7, 101, 101 aa-101 dd; 152; 165a-d) between the guide ends (6, 133 aa-133 dd, 134 aa-134 dd; 151 a, 151b; 170 a-f) is filled with an index matching liquid which has apredetermined refractive index, and the radiation-carrying core (8) ofeach radiation guide (49; 169 a-f) is designed to taper such thatradiation collimation (14) can be achieved by interaction with therefractive index of the index matching liquid and the free core profile(13) in the space (5, 135 aa-135 dd; 154; 171 j which is filled withliquid.
 2. The arrangement (4, 120) as claimed in claim 1, characterizedin that the refractive index of the index matching liquid is at most ofequal magnitide to the refractive index of each radiation guiding core(8), and the refractive index of the liquid is preferably between 99.90%and 98.00% with respect to the core refractive index, but is preferablychosen to be between 99.4% and 98.6%.
 3. The arrangement (4, 120) asclaimed in claim 1 or 2 having at least one radiation guide switch (2,100, 100 aa-100 dd; 166) which has a holder (19, 103; 166 a-d) forholding the switching part (7, 101, 101 aa-101 dd; 165 a-d) which can bemoved between the radiation guide ends (6, 133 aa-133 dd, 134 aa-134 dd;170 a-f), each holder (19, 103; 166 a-d) has at least one first combedstructure (23 a, 23 b; 115, 116) which is connected to it, a secondfixed-position comb structure (24 a, 24 b; 117, 119) which matches thefirst comb structure (23 a, 23 b) is provided, whose comb tines (24 a,24 b) are arranged with a gap with respect to the first structure (35),and a first and a second electrical voltage can be applied to the twocomb structures (23 a, 23 b, 24 a, 24 b; 115, 116, 117, 119) in order toproduce an electrostatic movement force, characterized in that each tineof at least one of the comb structures (23 a, 23 b, 24 a, 24 b) has inits free tine end region a region with a broadened cross section, inorder to hold the relevant comb structure with an electrostatic voltageapplied to it, and hence the switching part (7.2,101, 101 aa-101 dd; 165a-d) in a stable position.
 4. The arrangement as claimed in claim 3,characterized by at least one leaf spring element (51 a, 51 b, 52 a, 52b; 107, 109) which is firmly connected to the holder (19; 103), and onwhich the first comb structure (23 a, 23 b) is preferably in each casearranged, and, in particular, each leaf spring element (51 a, 51 b, 52a, 52 b) is designed such that it runs approximately at right angles tothe movement direction of the holder (19).
 5. The arrangement (4, 120)as claimed in one of claims 1 to 4, characterized in that each switchingpart (7, 101, 101 aa-101 dd; 165 a-d) has at least one surface (74 a, 74b) which acts as a mirror for the radiation of the radiation guide. 6.The arrangement in particular as claimed in one of claims 1 to 5,characterized in that the switching part (152) can be inserted into aradiation-carrying space (150) in the intermediate space (154) betweenin each case two guide ends (151 a, 151 b) in such a manner that thisresults in a predetermined attenuation of the radiation, in particularthe attenuating part (157) of the switching part (152) which can beinserted into the radiation-carrying space (154) being provided with ametal coating, and the angle between the attenuating part (157) and theflush axis (153) of the two guide ends (151 a, 151 b) preferably beingan angle of less than 65° and preferably of less than 50°, in order toreduce polarization-dependent attenuation caused by the insertedattenuated part.
 7. The arrangement as claimed in one of claims 1 to 6,characterized by a number of switching parts (165 a-d) in a radiationguide switch (166), in which case each switching part (165 a-d) can bepushed in front of in each case two radiation guide ends (170 c/170 d;170 b/170 d; 170 e/170 d; 170 f/170 d) of two radiation guides (169c/169 d; 169 b/169 d; 169 e/169 d; 169 f/169 d) such that radiationcoupling and/or attenuation are/is possible, and the switching parts(165 a-d) are preferably associated with the radiation guide ends (170a-d) such that output radiation from a number of radiation guide ends(170 a, 170 b, 170 c, 170 e, 170 f) can in each case be coupledindividually, depending on the switching position of one of theswitching parts (156 a-d), into a single radiation guide end (170 d)and/or, in particular, the output radiation from a single radiationguide end can in each case be coupled individually, depending on theswitching position of one of the switching parts, into one of theradiation guide ends.
 8. The arrangement (4, 120) as claimed in one ofclaims 1 to 7, characterized by a fluid-tight housing with fluid-tightbushings for the radiation guides and the electrical cables, with thehousing interior (86) being filled with the index matching liquid exceptfor a gas bubble (88), and the volume of the gas bubble (88) beingpredetermined such that any pressure in the housing interior (86) as aresult of thermal effects is not greater than or less than apredetermined value.
 9. The arrangement (120) as claimed in one ofclaims 1 to 8, characterized by a number of switches (100 aa-100 dd)which are arranged like a matrix in one plane, preferably on a firstchip, with this chip having in particular integrated electrical guidesubelements for electrical voltages which can be applied to the switches(100 aa-100 dd), and for the optical, and preferably the electricalconnections, a second chip, which is in the form of a waveconductor chipand is preferably applied using flip chip technology, is providedbetween the switches.
 10. A method for producing the radiation guideswitching arrangement (4, 120) having at least one radiation guideswitch (2, 100, 100 aa-100 dd; 166) which has a switching part (7, 101,101 aa-101 dd; 165 a-d), in which case the switch part (7.1, 7.2, 101,101 aa-101 dd; 165 a-d) can be moved in front of at least two radiationguide ends (6, 133 aa-133 dd, 134 aa-134 dd; 170 a-f) which lie in aplane, as claimed in one of claims 1 to 9, produced from a sandwichwafer (39) which has a substrate (70), a covering layer (73) and anelectrically insulating intermediate layer (71), characterized in thatthe radiation guide switching arrangement (4; 120) is produced from thesandwich wafer (70), inter alia with the switching part (7, 101, 101aa-101 dd; 165 a-d) and the guide channels (1.1 aa-1.1 d; 1.2 a-1.2 d,131) for the radiation guides (49; 121 a-121 d, 122 a-122 d; 169 a-f)and their ends (6, 133 aa-133 dd, 134 aa-134 dd; 170 a-f) by means of anetching process, during which at least one sacrificial web (75 a, 75 b)is in each case produced in the immediate vicinity of each of the outerfaces (74 a, 74 b), which run at right angles to the plane, of theswitching part (7, 101, 101 aa-101 dd; 165 a-d), in order to avoid theouter faces (74 a, 74 b) having a profile which differs from the normalto the plane.
 11. The method as claimed in claim 10, characterized inthat the sandwich wafer (39) has a covering layer (73) which is composedessentially of silicon and whose unmasked areas are removed in an ionetching process, with each sacrificial web (75 a, 75 b) being at adistance of approximately 10 μm, with a distance tolerance of −5 μm to+20 μm, for a covering layer thickness of approximately 73 μm with athickness tolerance of +/−3 μm.